Halogen lamps have become very popular, due in part to their relatively small size and their relatively high lumens with a relatively low wattage. However, the cost of halogen lamps remains high.
U.S. Pat. No. 5,610,469 to Bergman, the entire contents of which are incorporated by reference, discloses an electric lamp with an energy reflecting shroud disposed within a sealed envelope. The shroud is coated with an energy reflecting material, either on an inner or outer surface. The coated shroud comprises a ellipsoidally-shaped reflecting section and cylindrically-shaped end sections for mounting the shroud onto a bulb portion of an arc tube light source. Bergman does not pertain to a halogen incandescent lamp.
U.S. Pat. Nos. 5,221,876 to Bergman and 4,517,491 to Otto, the entire contents of which are incorporated by reference, disclose electric lamp with an energy reflecting shroud. While the shrouds reflect energy, the shrouds of each are not separate from the lamp itself, as they form a part of the lamp. The shrouds are seen to be needed for the complete assembly of the lamps. Further, the shrouds of each are not mounted on the lamp, but are mounted on a support of the lamp.
U.S. Pat. Nos. 4,535,269 to Tschetter, the entire contents of which are incorporated by reference, discloses a lamp with its inner bulb coated with an infrared reflecting shroud. As discussed hereinafter, while the lamp exhibits exceptional characteristics, the fill pressure of the lamp may be limited due to the location of the coating.
The cost of halogen lamps is based on several factors. However, there are at least two dominant factors involved with the pricing of halogen lamps. One of these dominant factors is a unit price of the quartz filament tubes. Another dominant factor in the cost of halogen lamps is the cost of an infrared radiation or light reflecting coating (hereafter "infrared reflecting coating") that is applied to interior surfaces of infrared halogen lamps. The infrared reflecting coating is intended to reflect energy back onto filaments of the lamp to heat the filaments. This heating of the filaments by reflected energy permits a more efficient efficacy, which is of course desirable.
In conventional surface coated infrared halogen lamps, only a portion of the inner surface will reflect energy back onto the filaments. However, the entire surface is coated with an infrared reflecting coating. Other than from a relatively small effective reflective area, coated areas of the tube will not reflect energy from the lamp onto the filaments. The energy from these other areas will merely be reflected to points either outside of the lamp or to parts of the lamp that will not benefit from the reflected energy. This ineffective reflection is an inefficient use of the coating. This waste of coating resources ultimately causes the cost of infrared reflecting halogen lamps to undesirably rise.
Further, conventional surface coated infrared halogen lamps are limited in the total fill pressure they can maintain due to the stress on walls added by the coating. This added stress limits the efficacy and life of such lamps, which is undesirable.